Method and apparatus for traversing blood vessels

ABSTRACT

Disclosed is a method for obtaining access to a relatively inaccessible region of a blood vessel for diagnostic or therapeutic purposes in which a primary catheter tube is inserted into the vascular system at an entry point remote from the relatively inaccessible region, the leading end of the tube is worked towards the inaccessible region in a conventional manner and then a secondary catheter tube contained within the primary tube is everted from the leading end of the primary tube to approach more closely to the required region. A catheter assembly for performing the method is also disclosed.

This is a divisional application of U.S. patent application Ser. No.022,219, filed Mar. 19, 1979.

BACKGROUND OF THE INVENTION

In recent years, special purpose catheter systems have been used totraverse and negotiate blood vessels for therapeutic as well asdiagnostic purposes. Therapy is delivered via catheters both as analternative to traditional surgery and as a means of last resort whensurgery is not possible. Thus, embolization of selected blood vessels issometimes performed in order to treat arterio-venous malformations andaneurysms, to block off the blood supply to tumors and to stop chronicbleeding. Other uses of catheters are to deliver chemotherapeutic agentsand other substances to highly localized areas and to sample body fluidsfrom remote spaces. More recently, balloon-type catheters have been usedfor treating stenoses in blood vessels as a means of relieving theconstriction by physically expanding the vessel in the region of astenosis.

Since the usefulness of the above forms of treatment is limited by theaccessibility of the lesion to be treated, efforts have been made todevelop catheters which can successfully penetrate ever deeper into thevascular system.

The basic problem is to advance a catheter through a narrow tortuousblood vessel without damaging the endothelium. Conventional cathetersare often too large to fit inside the desired vessel or too rigid tonegotiate the various twists and turns encountered in a particularvessel. Alternatively, they may be so flexible as to buckle instead ofadvancing into a remote vessel. Friction between the catheter and thevessel wall generally limits the length and number of curves throughwhich a catheter can be pushed and even with balloon tipped catheters,which take advantage of flow to pull the catheters through tortuousvessels, their travel is limited by wall friction. Magnetically guidedcatheters are similarly limited and their overall complexity and expenselimit their widespread application.

It is an object of the present invention to provide a method andapparatus for traversing blood vessels and which allows relatively deeppenetration of the vascular system even through narrow and tortuousblood vessels.

More particularly, it is an object of the invention to provide acatheter arrangement particularly suitable for the use in traversing ablood vessel and which at least partially overcomes the problemsassociated with earlier catheter arrangements used for this purposeparticularly as regards the matter of friction between the catheter andthe vessel wall.

It is a further object of the invention to provide a catheterarrangement for use in the vascular system which facilitates movement ofthe catheter through a narrow or tortuous blood vessel to obtain accessto relatively remote or inaccessible regions of the vessel.

Another object of the invention is to provide an improved method andmeans for traversing a blood vessel for therapeutic or diagnosticpurposes.

SUMMARY OF THE INVENTION

The invention is based on the concept of adapting the known principle ofan everting tube for use in a miniature catheter of a scale sufficientlysmall to negotiate a blood vessel.

An everting tube is a generally thin-walled flexible tube having aforward end attached to a circular opening in some form of housing, thetube being turned back inside itself to form a double-walled tube andthe rear end of the tube (the inner wall) being attached to a moveablemember within the housing. With this arrangement, an annular space isformed between the outer and inner walls of the tube. Thus, if themoveable member is caused to move towards the opening and pressure isapplied to the annular space, the inner wall of the tube will graduallyextend or evert from the opening, "turn the corner" and form an everlengthening outer wall. There is no movement of the outer wall as such,instead its length is progressively extended by the inner wall as itmoves out and "turns the corner". Further, the passageway defined withinthe inner wall can be used to carry liquid when pressure is releasedfrom the annular space.

The everting tube principle has previously been applied to catheters,see for example, U.S. Pat. Nos. 3,525,329, 4,043,345, 3,908,663,3,332,424, 3,911,927, 3,583,391, 3,669,099, 3,168,092, 3,433,215 and4,041,948, but such catheters have generally been intended for use inrelatively large-scale body passages and would not be suitable for usein an intravascular application requiring extensive penetration alongextremely narrow and tortuous vessels.

Two significant advantages over conventional catheters result from theeverting tube principle of operation. Firstly, since there is no bodilymovement of the outer wall of the tube, there is no relative motion andsubstantially no friction between the outer wall and the wall of thevessel through which it extends, and secondly, there is no need to makethe usual design compromise between catheter rigidity to avoid bucklingas it advances and catheter flexibility to negotiate sharp turns in thevessel.

Problems arise, however, in adapting the everting tube principle for usein a catheter system suitable for intravascular use which requires tubesof extremely small diameter (eg. ±1 mm.) and which need to travelrelatively long distances through tortuous blood vessels.

The force advancing the everting tube is proportional to the product ofthe area of the annulus between the inner and outer tube walls and thepressure P within this annulus and small size tubes require highpressure to provide enough force to evert the tube and make it advance.The advancing force must overcome (a) the resistance associated withbending forces where the tube everts or turns on itself, (b) frictionalforces of the uneverted portion of the tube sliding through the housingin which it is carried, and (c) frictional forces of the unevertedportions of the tube sliding within itself in the everted length. Thislast contribution arises mainly from internal contact forces resultingwhen pressure P is applied, causing the inner wall of the tube tocollapse into a ribbon-like form which tends to curl around to fit intothe outer wall. If the pressure P is increased too much to overcome theretarding forces, the tubing tends to balloon and burst and if the wallthickness of the tube is increased too much, to prevent bursting, thetube may not readily evert.

In accordance with the present invention, the everting tube principle isapplied to an intravascular catheter system by utilizing the tube as asecondary catheter which everts from the leading end of a primarycatheter tube. Thus, in use, the primary catheter tube of generallyconventional form with the everting tube carried completely inside ofit, is inserted into and worked through a blood vessel in theconventional manner and when the leading end of the primary tube hasreached the limit of its travel, due either to further inaccessibilityor length of travel, the everting tube, having its forward end attachedto the leading end of the primary tube, is everted from the leading endof the primary tube for further advancement along the blood vessel.

Further in accordance with the invention, to reduce the frictionproblems associated with everting tubes of small diameter, as outlinedabove, the everting tube is made in a particular form, namely the tube,which preferably is extruded from a strong flexible synthetic plasticmaterial and coated with an anti-friction coating, is heat set into across-sectional form which ensures that when everted, the inner wallsection will fit naturally within the outer wall section withoutexcessive contact force when pressure is applied in the annulustherebetween. Preferably, the tube is heat set to provide a crosssection having an indented profile, such as a U-shaped or cruciformprofile, the former profile being preferred. Then, in use, the unevertedlength of the tube, the inner wall section, retains its heat setindented form while the everted length of the tube due to pressure inthe annular space between the sections opens to its naturalsubstantially circular cross-sectional form. After complete eversion ofthe tube, when pressure is released from the annular space and fluid ispassed through the central tube passageway within the uneverted length,this uneverted section will, in turn, open out to assume the naturalcross-sectional form due to the fluid pressure within it.

Other features of the invention will become apparent from the ensuingdescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view through the forward end of acatheter system incorporating an everting tube and showing the evertingtube in a partially extended condition;

FIGS. 2 and 3 are sections on lines 2--2 and 3--3 of FIG. 1,respectively;

FIG. 4 is a view similar to FIG. 1, showing the everting tube in a fullyextended condition and with its inner wall inflated;

FIGS. 5 and 6 are sections on lines 5--5 and 6--6 of FIG. 4,respectively;

FIG. 7 is a perspective view of a complete catheter assembly;

FIG. 8 is a cross-sectional view of part of the assembly shown in FIG.7; and

FIG. 9 is a composite cross-sectional view of the entire assembly shownin FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As best shown in FIG. 7, the principal components of the illustratedcatheter assembly are a primary catheter tube 10 and an everting tube12, these being the components which actually enter the vascular systemof a patient and the assembly being completed by ancilliary equipmentremaining external to the patient's body and including an extension tube14, a manifold 16, syringes 18 and 20 for applying pressure fluidrespectively to the outer annulus of the everting tube and to itsinternal passageway, and a pressure gauge 22 for measuring the pressureof the former fluid. In use, the primary catheter tube 10 with theeverting tube 12 fully contracted therewithin is inserted into thevascular system and worked along a blood vessel in the conventionalmanner. Then, when the leading end of the tube 10 has reached its limitof travel through the blood vessel, tube 12 is everted from within tube10 for further advancement of the catheter along the vessel.

Tube 10 is a conventional form of flexible catheter tubing used forintra-vascular applications for example, a polyurethane tube of 2.15 mm.outside diameter, 1.4 mm. inside diameter and 1 meter long, the tubehaving its inner surface treated with a friction reducing hydromercoating. The leading end of tube 10 is tapered (FIG. 9) and the forwardend of everting tube 12 is fused or welded to the outer surface of tube10 at the leading end along with a protective cap 24. The trailing endof tube 10 is bonded to the extension tube 14, conveniently also ofpolyurethane and having an outside diameter of 3.8 mm., an insidediameter of 3.12 mm. and a length of 0.6 meters.

Everting tube 12 is likewise extruded in polyurethane and has, forexample, an outside diameter of 1 mm., a wall thickness of 1/15 mm. anda length of 1.6 meters. This tube has its outer surface covered with afriction reducing hydromer coating, and after extrusion, is heat set toprovide an indented cross-sectional profile, preferably a substantiallyU-shaped profile, as shown in FIGS. 2 and 3, although other indentedprofiles such as a cruciform profile are also considered suitable. Heatsetting of tube 12 may, for example, be effected by winding the tubearound a helically grooved or ridged heated drum, whereby the ridge inthe drum provides the required indentation in tube 12.

As indicated, the forward end of tube 12 is opened out, turned back onitself and welded or fused to the leading end of tube 10 at point 10aunder protective cap 24, while the main body of tube 12, the unevertedlength or inner wall, is taken back through tube 10 and its rear end isbonded around the opening at the forward end of an axially moveableplastic support tube 26. This forward end of tube 26 is also tapered andprovided with a slit section 28 formed from one or more slits whichserves as a valve arrangement for preventing tube 12 from being pushedback through tube 28. The flaps so created by the slit or slits areinwardly deflected by the pressure in the annulus thus producing anobstruction to rearward motion of the secondary tube. Further, theforward end of tube 26 is provided with caps 30 and 32 serving toprevent tube 12 from working back along the space between tubes 14 and26. The rear end of support tube 26 is attached to a sliding metalcoupling arrangement 34, to the rear of which is welded a steel tube 36which extends back through the manifold 16 and carries a connection 38for the syringe 20.

Extension tube 14 is at its rear end attached to a metal coupling 40connected to the manifold and the manifold has passages 42 and 44connected respectively to syringe 18, via a tap 46, and pressure gauge22. Syringe 18, thus, communicates via passage 42, coupling 40 andextension tube 14 with the interior of primary catheter tube 10, i.e.,with the annular space surrounding the inner wall of the everting tube12.

Operation of the device is as follows:

With the everting tube 12 and steel tube 36 in the fully retractedcondition, tube 10 is introduced into the vascular system at a suitableentry point and worked through a blood vessel in the conventional mannerunder fluoroscopic observation until it is advanced to its full lengthor until an obstruction is encountered or until friction impedes itsfurther advance. Then, steel tube 36 is advanced slightly to provideslack in the everting tube. Pressure at about 1.7 to 2 atmospheres isapplied to the annular space surrounding the inner wall of tube 12through syringe 18, causing eversion of tube 12 from the leading end oftube 10 until the slack in tube 12 is taken up, this process again beingperformed under fluoroscopic observation. The fluid used for evertingtube 12 is conveniently a standard X-ray contrast media which allows theoutline of tube 12 to be viewed under X-ray. Tube 12 thus extends fromthe leading end of tube 10, and when the slack in tube 12 is taken up,the steel tube 36 is further advanced and the process is repeated. Thisprocedure is continued until the everting tube has reached its maximumextension, or until the target region of the blood vessel has beenreached.

During eversions of tube 12, when pressure is applied through syringe18, the inner wall or uneverted section of tube 12 retains its indentedcross-sectional profile, FIGS. 2 and 3, while the everted outer wall isexpanded to the normal substantially circular cross-section of the tube.

When the maximum or required degree of eversion has been obtained,pressure in the annular space surrounding the inner wall of tube 12 canbe relaxed and the inner passageway of tube 12 is then available for theapplication of fluid under pressure to the target region of the bloodvessel via the steel tube 36 and syringe 20. Under the influence of suchpressure fluid, the inner wall of tube 10 is then expanded to itsnormal, substantially circular cross-section, as shown in FIGS. 5 and 6.Alternatively the everting tube can be used to transport any objectthrough the blood vessel for diagnostic or other purposes e.g., acatheter guide wire or a small fluid sampling tube.

After treatment has been terminated, the catheter can be withdrawn byreleasing pressure from both syringes, retracting steel tube 36, so thattube 12 is itself again retracted into tube 10 and then withdrawing tube10 from the blood vessel in the normal way.

It will be appreciated that a catheter assembly as herein described andits method of application, is suitable for use in effecting entry torelatively inaccessibly regions of the vascular system for eithertherapeutic or diagnostic purposes. Where the catheter is to be used fortreating stenoses by physical expansion of the vessel in the region ofthe stenoses, tube 12 may be provided with sections of differingdiameter and in use, the apparatus can be manipulated in such a way thata diameter suited to expand a particular region of the vessel isavailable for use at the required location and the tube 12 beingexpansible under elevated pressure for this purpose.

Advantages of attaching the secondary tube to the distal end of theprimary tube as opposed to having it originate from outside the body aretwo-fold: (a) there is less required distance for the secondary tube tobe everted e.g., 0.3 m as to 1.3 m and therefore far less frictionbuild-up and required everting pressures, (b) the reduced requiredtravel of the proximal end of the secondary tube makes practical anaxial feed arrangement (as opposed to winding the secondary tube on adrum) which in turn enables the lumen of the secondary tube to remainopen more reliably.

While only a single embodiment of this invention has been described indetail, it will be appreciated that numerous modifications are envisagedwithin the scope of the invention as defined in the appended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A catheter assembly forinsertion at least a predetermined distance into a body passage of aliving being, said assembly comprising:first means for inserting saidassembly into and through said body passage a distance which is lessthan said predetermined distance, said first means comprising anenlongated transversely flexible primary catheter tube having an openleading end and a trailing end, said primary catheter tube furtherincluding an insertable portion adapted for insertion longitudinallyinto said body passage, said insertable portion including and extendingrearwardly from said leading end and being circumferentially closed andcontinuous throughout its entire length, said primary catheter tubebeing sufficiently transversely flexible to conform to bends in saidbody passage; second means for providing access for said assembly to atleast said predetermined distance of said body passage, said secondmeans comprising a secondary everting catheter tube of substantiallygreater flexibility than said primary catheter tube and having a forwardend and a rearward end, said secondary catheter tube being normallydisposed in a quiescent position substantially entirely within saidprimary catheter tube to permit the catheter assembly to be insertedinto said body passage with the secondary everting catheter tubeuneverted and retracted in said quiescent position, said forward endbeing sealed and secured to a connection region on the insertableportion of said primary catheter tube to define an elongated spacebetween the primary and secondary catheter tubes interiorly of saidprimary catheter tube, said elongated space being closed at one end bysaid connection region; and everting means for selectively everting saidsecondary catheter tube from said quiescent position within said primarycatheter tube forwardly and outwardly from the leading end of saidprimary catheter tube, said everting means comprising first pressureapplying means for supplying eversion-inducing pressurized fluid to saidelongated space.
 2. The catheter assembly according to claim 1 furthercomprising support means for said secondary everting catheter tube, saidsupport means being attached to said rearward end and axially movablewith respect to said primary catheter tube, said support meanscomprising a support tube having a leading end attached to said rearwardend of said secondary everting catheter tube.
 3. The catheter assemblyaccording to claim 2 wherein uneverted portions of said secondaryeverting catheter tube define an interior passageway, said assemblyfurther comprising second fluid pressure applying means for supplyingfluid under pressure through said interior passageway, said second fluidpressure applying means comprising supply means communicating with saidsupport tube to deliver fluid under pressure through said support tubeto said interior passageway.
 4. The assembly according to claim 3wherein said supply means comprises a further tube communicating withthe trailing end of said support tube, and a connection on said furthertube for a pressure fluid supplying syringe means.
 5. The assemblyaccording to claim 4 wherein said support tube is formed from resilientmaterial; andwherein the leading end of said support tube includes meansfor preventing said secondary tube from being drawn back into saidsupport tube, said means for preventing comprising at least onenon-return valve-like slit in the leading end of said support tube. 6.The assembly according to claim 1 wherein said secondary evertingcatheter tube includes an outer surface which, when uneverted, faces aninterior surface of said primary catheter tube; andwherein said interiorand outer surfaces are each covered with a friction-reducing coating. 7.The assembly as defined in claim 3 wherein the uneverted portions ofsaid secondary everting catheter tube include radially inner and outersections, assembly further comprising means for minimizing contact andfriction between said radially inner and outer sections of saidsecondary everting catheter tube, said means for minimizing comprising apermanently set cross-sectional profile of said tube, said profile beingsuch that said inner and outer walls, when non-everted, are mutallyspaced and have curved open-sided configurations, one within the other.8. The assembly as defined in claim 3, wherein said support tube iscontained within an extension tube attached to said trailing end of saidprimary tube.
 9. The assembly as defined in claim 8, including meansoperative in a space between said support tube and said extension tubefor preventing said secondary tube from being drawn back into saidspace.
 10. The assembly as defined in claim 9, wherein said meansoperative in said space comprises protective cap means secured to theleading end of said support tube.
 11. The assembly as defined in claim8, including manifold means communicating with said extension tube, saidfirst pressure applying means including a syringe connection associatedwith said manifold means and passage means in said manifold meanscommunicating with said substantially annular space via said extensiontube.
 12. The assembly of claim 7, wherein the cross-sectional profileof said secondary tube is permanently set into a substantially U-shapedform.
 13. The assembly of claim 3, wherein said primary tube and saidsecondary tube each have a sufficiently small diameter for passagethrough a blood vessel.
 14. A catheter assembly including:a hollowmember having one end formed with an opening; an everting catheter tubehaving a forward end and a rearward end; means securing said forward endproximate said opening in said hollow member; wherein said tube isturned inside of itself from said forward end and extends back throughsaid hollow member to form a radially inner section which becomes aradially outer section as the tube is everted from said opening; supportmeans for said tube attached to said rearward end of said tube, saidsupport means being movable relative to said hollow member toward andaway from said opening; pressure applying means for supplying fluidunder pressure to a space defined internally of said hollow memberaround said tube to evert said tube from said opening; and means forminimizing contact and friction between said inner and outer sectionsduring eversion of said tube, said means for minimizing comprising apermanently set cross-sectional profile of said tube when not everted,said profile being such that said inner and outer sections are mutuallyspaced and have curved open-sided configurations, one within the other.15. The improvement of claim 14 wherein said everting catheter tube hasan outer surface which, when uneverted, faces an interior surface ofsaid hollow member, and wherein said interior and outer surfaces areeach covered with a friction-reducing coating.
 16. The assembly asdefined in claim 14, wherein the cross-sectional profile of said tube ispermanently set into a substantially U-shaped form.
 17. The assembly asdefined in claim 14, wherein said hollow member is a further flexiblecatheter tube having a leading end and a trailing end and wherein saidforward end of said everting tube is secured proximate said leading endof said flexible tube.
 18. The assembly as defined in claim 14, whereinsaid everting tube and said flexible tube are each sufficiently small incross-section for passage through a blood vessel.
 19. The assembly ofclaim 18, wherein said everting tube has a diameter of the order of 1mm. and said flexible tube has a diameter of the order of 2 mm.
 20. In acatheter assembly including a hollow member having one end formed withan opening, an everting catheter tube having a forward end and arearward end, said forward end being secured proximate said opening insaid hollow member to form a radially inner section which becomes aradially outer section as the tube is everted from said opening, saidtube being turned inside of itself from said forward end and extendingback through said hollow member, support means for said tube attached tosaid rearward end of said tube, said support means being movablerelative to said hollow member toward and away from said opening,pressure applying means for supplying fluid under pressure to a spacedefined internally of said hollow member around said tube for evertingsaid tube from said opening, the improvement wherein the cross-sectionalprofile of said tube is set such that said radially inner and outersections are mutually spaced and have curved open-sided configurations,one within the other, wherein said support means comprises a supporttube having a leading end and a trailing end, said rearward end of saideverting tube being secured proximate said leading end of said supporttube, and the assembly including further pressure applying means tubefor passage through the interior of said everting tube.